The invention relates to a digital tachometer having stationary wire pulse sensors that are separated from a magnet equipped generator wheel by an air gap. Such a tachometer requires accurate adjustment of the air gap between the wire pulse sensors and set and reset magnets mounted on the circumference of the generator wheel. This adjustment has been complex and difficult. For this purpose several sensors mounted in series as viewed in the circumferential direction of the generator wheel housed in a sensor cassette which extends over a portion of the generator wheel have been used. A need exists for a tachometer of this type in which the separation between the wire pulse sensors and the generator wheel is established in a simple and reliable manner.